1. Field of the Invention
The present invention relates to drilling and/or striking hammers having lubricating devices.
2. Description of the Related Art
In drilling and/or striking hammers, designated as hammers below, it is known that various moving parts of the hammers require lubrication. For example, hammers have a transmission that transmits power from a drive motor to a percussion system and that has numerous bearings and toothed gears that require lubrication. Components of the hammer's percussion system also require lubrication. As an example, the typical hammer has a tool shank that is housed in a tool holder that is impacted by a reciprocating striker in use. The upper of the tool shank requires lubrication during use.
It is also known that housings of such lubrication-requiring components are typically not fully sealed units that can hold and maintain a volume of lubricant indefinitely. Instead, the hammer consumes lubricant during use as small quantities of lubricant leak from the transmission, percussion system, and/or the tool holder. The lubricant must be periodically replenished to maintain adequate lubrication of system components.
At any given time, the amount of lubricant in a hammer is not readily visually or otherwise discernable. Accordingly, lubricant replenishing is usually performed according to a maintenance schedule that provides recommended service intervals as functions of tool use periods. As an example of a recommended service interval, lubricant replenishing or refilling is typically performed after each twenty operational hour interval. Such twenty hour operational interval is an average time, following a lubricant refill, that a hammer will consume enough lubricant to leave only a minimum volume of lubricant to suitably lubricate the hammer.
Rates of lubricant consumption can vary dramatically as functions of, for example, temperatures of the transmission system, percussion system, and/or tool holder. This is because many lubricants, particularly grease, become progressively less viscous as their temperatures rise and leak from the hammer at a higher rate. Transmission system, percussion system, and/or tool holder temperatures can be influenced by both tool use intensity and ambient temperature. Hence, low intensity tool use and/or low ambient temperatures can lead to relatively low rates of lubricant consumption, while high intensity tool use alone or in combination with high ambient temperatures can lead to particularly high rates of lubricant consumption. The recommended maintenance schedule for refilling the lubricant of most hammers is based on average consumption rates. A user therefore may refill the lubricant more frequently than is actually required if a hammer consumes lubricant at a particular low consumption rate. Stopping use of a hammer to refill lubricant more frequently than is required can lead to lower production efficiency of the tool. Conversely, if a hammer consumes lubricant at a particular high rate, then a user may refill the lubricant less frequently than is actually required. This can lead to rapid wear of hammer components and premature failure.
In addition to running out of lubricant, a lubricant starved condition can be momentarily imposed on a hammer due to its lubrication system's configuration. This can occur, for example, if lubricant dispensing takes place randomly and/or if dispensing is position dependent or influenced. Exemplary of a drilling and/or striking hammer of this sort can be seen in a German Patent No. DE 39 36 849 A1. There, in a cover a depression is formed in which a high-viscosity grease is contained that can gradually flow through a dosing opening into a glide bearing between a crank bolt and a connecting rod. The dispensing of the lubricant takes place randomly, and is possible only when the hammer is in a suitable position, because gravitational support is required.
In European Patent Application No. EP 0 861 997 B1, a hand tool having a lubricated angular gear is described. There, a reservoir of lubricant is provided in the form of a pot that is open at the top, through which there passes a rotating spindle shaft. In the pot, a metal ball can move in such a way that due to the housing vibrations it tumbles through the lubricant, which is likewise located in the pot. In the base of the pot, a dosing opening is provided through which lubricant is occasionally pressed downwards due to the random motion of the metal ball; in this way, the lubricant reaches a ball gear for lubrication. Here as well, the lubrication takes place randomly and cannot take place independent of position.